Saw a couple of tweets circulating around this issue and would like to extend it to others. For those who are using vCenter Server Appliance, there is a default password expiration which is set at 90 days. This is enforced to all local accounts including root. If you have deployed vCSA 5.5, you are likely to hit the expiry soon or have already hit the expiry. I quickly checked my vCSA and guess what, I can’t login anymore.
A KB article has been released to address this issue. Link is here
The KB article is straightforward and easy to follow and I was able to reset my root password without issues. The Admin tab of the vCSA GUI allows you to change the expiration or disable expiration at all.